The present invention relates to an apparatus and a method for molding articles.
Typical vehicle steering wheels are formed by molding. When molding a steering wheel, a core is arranged at a predetermined position in the cavity of a mold. The cavity is then filled with molding material. A reaction of the molding material occurs in the mold and the material is cured. The molding material for steering wheels typically contains polyurethane (PUR) as a foaming agent. However, some polyurethane used as a foaming agent for steering wheels has poor light resistance and yellows with time. Therefore, when using polyurethane for molding an article, the surface of polyurethane portion of the molded article is coated with surface protection having light resistance, or a mold coating agent, to form a mold coating agent layer.
Such a mold coating agent layer is formed, for example, in the following manner.
Preparation of the molding is usually performed in one of the two following methods. According to one of the methods, a solution containing mold coating agent and a solvent, or a coating material, is poured into the recesses of a mold when the mold is open. Then, the core is arranged to correspond to a cavity, which is defined by the recesses when the mold is clamped. According to the other method, the core is first arranged to correspond to the cavity. Then, coating material is poured in to the cavity after the mold is clamped.
In either method, after the coating material and the core are arranged in the mold, air in the cavity is discharged through a discharging hole, which communicates the cavity with the exterior of the mold. Accordingly, the interior of the cavity becomes vacuum. The vacuum causes the solvent in the coating material to boil. As the solvent boils, foams are created and broken, which scatters the mold coating agent. This applies the mold coating agent to the inner wall of the cavity. The applied agent is then dried. Thereafter, the cavity is filled with the molding material to form a urethane article.
However, according to the prior art method, some of the molding material flows from the cavity to the exterior of the mold through the discharging hole. The flowing out molding material is hardened and creates scrap. Also, when molding a urethane article, the amount of molding material poured into the cavity needs to be increased to factor in the outflow of the molding material through the discharging hole. Accordingly, the cost of the molded articles is increased.
When the pressure in the cavity is lowered, some of the coating material, which has been poured into the cavity, is discharged through the discharging hole. Therefore, the amount of the coating material poured into the cavity needs to be determined by factoring in the amount of the coating material that is discharged when the cavity pressure is lowered. This increases the cost of the coating material and thus increases the costs of the molded article.
To prevent the molding material and the coating material from flowing out of the mold, the size of the discharging holes may be reduced. However, if the size of the holes is extremely reduced, polyurethane in the molding material and the mold coating agent in the coating material will be hardened in the holes and blocks the holes. If the discharging holes are blocked, the scattering of the mold coating agent and the sublimation of the solvent in the coating material are hindered. Thus, the mold coating agent cannot be sufficiently dried. Also, the mold coating agent cannot be applied evenly.